Republican and Democratic lawmakers expressed concern Sunday over President Donald Trump's declaration of a national emergency to divert money to build his proposed border wall after Congress refused to authorize such funding.

The declaration, which Trump made Friday, has divided Republicans, with some saying the move amounted to constitutional overreach and could open the door to a future Democratic president declaring similar emergencies over issues the GOP disagrees with.

Speaking on NBC's "Meet the Press," Republican Sen. Ron Johnson of Wisconsin, chairman of the Senate Homeland Security and Governmental Affairs Committee, said "many of us are concerned about" the declaration.

That declaration is "certainly the expansion of authority Congress has given past presidents; this president has the same authority," Johnson said. "I wish he wouldn't use it in this case. But again, I understand his frustration."

Johnson said he would take "a very careful look at what he's doing here in this instance."

"I'm going to take a look at the case the president makes," Johnson said. "And I'm also going to take a look at how quickly this money is actually going to be spent versus what he's going to use.

"If he's not going to be spending it this fiscal year or very early in the next fiscal year, I would have my doubts" about whether the situation at the border is truly an emergency, Johnson continued. "So again, I'm going to take a look at it and I'll, you know, I'll decide when I actually have to vote on it."

On Friday, Trump ordered a national emergency to build a border wall that he could not get Congress to fund. The government is fresh off of a 35-day partial government shutdown — the longest in U.S. history — that began after lawmakers refused to provide Trump with $5.7 billion in funding to build that wall. Trump shut down the government in response, but relented after more than a month, signing a stopgap spending bill.

The president on Friday also signed a bipartisan spending agreement that included more than $1.3 billion for 55 new miles of border fencing as well as money for other border security measures. Trump will now try to divert nearly $7 billion from a combination of military construction projects, counternarcotics programs, and a Treasury Department asset forfeiture fund to build a longer border barrier.

The national emergency has already drawn legal challenges, which Trump said he expected in announcing the emergency on Friday. He also said he declared the emergency not out of necessity, but to facilitate quicker wall building.

"I could do the wall over a longer period of time," Trump said. "I didn't need to do this. But I'd rather do it much faster."

Congress could pass a resolution disapproving of the emergency declaration, which it has the power to do under the 1976 National Emergencies Act.

On CBS's "Face the Nation," Republican Rep. Will Hurd of Texas, who represents a border district, said he would support such a resolution and said he did not think a national emergency declaration was necessary.

"That is not a tool that the president needs in order to solve this problem," he said.

Democrats voiced strong opposition to Trump's move. On ABC's "This Week," Democratic Sen. Tammy Duckworth of Illinois said the House should sue Trump if the resolution is not veto-proof.

"Frankly, the president is trying to take the power of the purse away from the legislative branch," she said. "We are co-equal branches of government and he is trying to do a type of executive overreach, and it's just really uncalled for."

Speaking with CNN's "State of the Union, Democratic Sen. Sherrod Brown said the declaration was in violation of the Constitution.

"Well, this is the first kind of emergency we have seen like this that a president has done this," he said. "He couldn't get the Mexicans to build the wall. He couldn't get Congress to vote the money in. ... That's why you see so many Republicans saying don't do this. Republicans are afraid that he's going to take the money from somewhere else and something they care about, but, fundamentally, they think it's a president who failed, who hates to lose, who is acting childish."

But others took to the airwaves to defend the president. Republican Rep. Jim Jordan of Ohio told "This Week" that the declaration was necessary because Congress would not fund the president's priority.

"So we tried to do it the appropriations process way and get building it," Jordan said. "We tried to do this last year, and our party, our party leaders wouldn't even go there, Democrats certainly wouldn't go there. So yes, it's going to be a slow process, it's going to go to the courts. We understand that. But better to start that process so that we can ultimately get there than to not start it at all."

Republican Sen. Lindsey Graham of South Carolina told "Face the Nation" that the southern border is a national emergency.

"Let's just say for a moment that he took some money out of the military construction budget," Graham said. "I would say it's better for the middle school kids in Kentucky to have a secure border. We'll get them the school they need. But right now we've got a national emergency on our hands."